The implantation of stents has established itself as one of the most effective measures for the treatment of vascular diseases. Stents have the purpose to take on a support function in the hollow organs of a patient. One of the main application areas of such stents is to permanently or temporarily widen and keep open vascoconstrictions, in particular constrictions (stenoses) of the coronary vessels. Apart from that, for example, aneurysm stents are known which serve for supporting damaged vascular walls. Stents of conventional design have a tubular base body with a filigree support structure of metallic struts, wherein said base body, for insertion into the body, is initially present in a compressed form and expands at the site of application. For placing stents, usually, catheters having an inner hose and an outer hose are used as an application device. It is possible here to use different catheters having inner and outer hoses.
For the application of self-expandable stents, balloon catheters are most commonly used. For this, the stent is mostly fixed by means of so-called “crimping” on a surface of the non-dilated balloon situated on the inner hose of the catheter and is protected against damage during the positioning of the catheter by overlapping with an outer hose. After the balloon catheter carrying the stent has been inserted into the vessel and the stent has reached the site of the intended application, the outer hose is drawn back and the balloon dilates. Thereby, the stent is expanded and to contact the vascular wall. Once the stent has been sufficiently widened and the vessel has been sufficiently expanded, the pressure in the balloon is reduced, the balloon returns to a non-dilated state and the catheter can be removed again, whereas the applied stent remains in the vessel and keeps the same open. Suitable balloon catheters for stent application are well known and are described exemplary in DE 102 15 462.
Alternatively, a self-expandable stent design can be used. Application devices for applying self-expandable stents usually do not have a dilatable balloon for stent application. Here, mostly catheter devices are used which have an inner hose and an outer hose, wherein the stent to be applied is initially fixed or crimped onto a surface of the inner hose and covered by an outer hose slid thereon. In the crimped form, self-expandable stents have a radial force which presses the outer surface of the stent against the outer hose's inner surface covering the stent. The catheter is introduced into the vessel until the stent reaches the site where the stent is to be applied. For application, the outer hose is now drawn back until the entire stent is exposed. Due to the radial force, the stent expands automatically, becomes detached from the inner hose and contacts the vascular wall. Once the stent has sufficiently dilated, the catheter can be removed again whereas the applied stent remains in the vessel and keeps the same open. Suitable catheters for the application of self-expandable stents are well known and are described exemplary in U.S. Pat. No. 5,824,041.
One problem of these catheters having an inner and an outer hose is that during positioning the catheter in the vascular system of the patient, uncontrolled and sometimes high loads act on the distal end of the inner and outer hoses. This can in particular result in that the hose wall at the distal end of the outer hose is irreversibly stretched and a so-called “fish mouth” is formed. Said “fish mouth” formation can contribute to injuries of the vascular wall during the application of the catheter as well as during the removal of the catheter and can result in malfunctions during catheter positioning.